XPS for chemical- and charge-sensitive analyses

TLDR: In this paper, the X-ray photoelectron spectroscopic binding energy shifts, while subjecting samples to a variety of optical and electrical stimuli, information about charge accumulation on materials or surface structures can be obtained.

About: This article is published in Thin Solid Films.The article was published on 2013-05-01 and is currently open access. It has received 40 citations till now. The article focuses on the topics: X-ray photoelectron spectroscopy & Photoconductivity.

Figures

Fig. 8. Schematic representation of band-bending in SiO2/p-Si and SiO2/n-Si interfaces. B.E. and K.E. refer to binding and kinetic energies, respectively, and SiOx Ind. refers to the potential induced by the oxide layer.

Fig. 1. Schematic diagram of the XPS technique. Note that the measured binding energy (B.E addition to its elemental nature and chemical state (chemical shift).

Fig. 11. (a) XPS spectra of the Si2p region of a SiO2/p-Si sample connected to ground (green) the bottom, after correcting for the 10 V bias. The thickness of the silica overlayer is ~8 nm

Fig. 12. XPS spectra of the Si2p region of a p-n junction Si-diode recorded; under: 0 bias, −8 V forward, and +8 V reverse bias. The inset schematically displays the electrical connections [50].

Fig. 10. The In3d5/2 and Ga2p3/2 peaks recorded while the In0.45Ga0.55N sample is subjected to illumination with different lasers. The photoinduced shifts in Ga peak are more pronounced compared to that in the In peak.

Fig. 17. Cd3d XPS spectra from a CdS film with and without 405 nm photoillumination, and under (a) 10 kHz and (b) 0.001 Hz square-wave electrical stresses. The intensity of excitation source is tuned with a neutral density filter (NDF).

Frequently asked questions

Q1. What are the contributions mentioned in the paper "Xps for chemical- and charge-sensitive analyses" ?

In this paper, it was shown that by combining d.c.c and a.c., the interatomic and intermolecular delocalization of electrons becomes important for more intelligent utilization of these materials ; for creating artificial muscles, and adaptive optical devices, such as lenses and diffraction gratings ; mechanical actuators for control of tactile patterns of Braille interfaces ; electrically refreshable displays ; better control of photogeneration of charge in electro-photography, and xerography ; design and fabrication of supercapacitors. 

Q2. What is the effect of XPS on the n-type sample?

Exposure of insulating materials to energetic particles like γ-rays, X-rays, and UV photons creates long-lasting defects such as colorcenters, resulting in modification of the electrical properties of these materials, which can also be probed by XPS. 

Q3. What is the advanced tool for probing the charge at submicron dimensions?

Kelvin probe atomic force microscopy (KP-AFM) has been the most advanced analytical tool for probing, quantifying, and mapping the charge developed at submicron dimensions [21]. 

Q4. What is the effect of negative biasing on the charge of the oxide?

Note that upon negative biasing, the positive charging of the oxide increases since all of the neutralizing lowenergy electrons from the flood-gun and/or other sources are repelled. 

Q5. What is the simplest fundamental unit of modern electronic and photovoltaic devices?

A p-n junction, the simplest fundamental unit of modern electronic and photovoltaic devices, was examined by XPS during operation. 

Q6. What is the description of a semiconducting bulk material?

Semiconducting bulkmaterials are best described by filled valence and empty conduction bands with an energy separation or band gap Eg. 

Q7. How long did it take to remove the protective coating?

The authors have used a commercially available Si-diode (1N 4007) after mechanically removing the protective polymer coating and sputter etching the device with a (1 keV, 15 μA) Ar+ ion-gun for ~10 minutes. 

Q8. What is the effect of the square wave excitation on the Cd3d peaks?

At the higher frequency, the Cd3d peaks split at ±10 V, display uniform shifts, with respect to the laser intensity, as the result of photoconductivity changes. 

Q9. What is the effect of the light source on binding energy shifts?

For photoactive materials such as CdS and GaN, binding energy shifts are additionally influenced by both the wavelength and the intensity of the light source used for illumination. 

Q10. What are the common factors contributing to charge accumulation on materials and/or surfaces?

There are a myriad of chemical, physical, thermal, optical, mechanical phenomena contributing to charge accumulation on materials and/ or surface structures, all amenable to charge sensitive XPS analysis. 

Q11. What is the binding energy difference between the two peaks?

As shown in the figure, the binding energy difference between the split oxide peaks is 20.00 eV at the higher frequency of square-wave excitation, but is smaller at the lower frequency, in contrast to Si0, which is 20.00 eV at both frequencies. 

Q12. What is the effect of long lasting UV radiation on SiO2?

As shown in Fig. 9, longlasting charging effects on SiO2 surfaces induced by 254 nm UV radiation (6 Watts, low pressure Hg lamp) causes shifts in the XPS peak positions. 

Q13. What is the effect of the frequency-dependent response?

Through analysis of the frequency-dependent response, it is possible to determine the chemical as well as physical (ions, dipoles, electron–hole pairs, etc.) nature of the photoactive sites and/or defects. 

Q14. How can the authors measure the polarity of the charge and/or photovoltage shifts?

The authors have shown that by combining d.c. and a.c. electrical and optical stimuli to the sample, while recording XPS spectra, polarity and frequency dependence of the charging and/or photovoltage shifts can be probed covering a wide frequency range from 10−3 to 106 Hz. 

Q15. What is the process of incorporating charges on a conducting sample?

A trivial and controlledway of incorporating charges on a conducting sample is by connecting it to an external voltage source (i.e., a battery or a power supply). 

Q16. What is the process of creating electron and hole pairs?

The conventional description of this process is by use of band-diagrams, indicating creation of electron and hole stateswithin the bandgap of semiconductors.